Grinding mill



Aug- 30 1932- H. HARDINGE 1,87%985 GRINDING HILL Filed July 22, 1929 5 Sheets-Sheet 1 Aug 30 1932- H. HARDINGE 1,874,985

GRINDING MILL Filed July 22. 1929 5 Sheets-Sheet 2 Snowdon /YARLOWE MM2/N65 lhIg. 30, 1932. H HARDlNGE 1,874,985

GRINDING HILL Filed July 22, 1929 5 sheets-Sheet 3' .Ha/now: fluo/N65' `v`rUNITED ASTATES 'PATENT OFFICE INCORPORATED,IOF YORK, PENNSYLVANIA, A CORPORATION OF NEW YORK GRINDING MILL Application yfiled July 22,

'This inventionV relates to grindingimills,

4.and more'partieu-larly todischarge `means V therefor.

.Oneof theobjects of the invention is vto provide discharge means at the discharge end of agrinding mill which will operate to strain the pulp carrying pulverizedv material from the mill. and permit the same to pass lil out ofthe mill, while at the Sametime operating to: returnballs and oversize material `which comes 1n contact therewith.

eA-nother object of the invention is to pro- .vide discharge means inthe form of vanes i vwhich are carried vby the mill during its .rotation andwhich are so constructed as to tact therewith.

Another 'object of the invention is to provide discharge means offering substantiallyr fnore'striction to the flow of material from 'the grinding zone to the discharge end of the mill.

Another object ofthe invention is to provide discharge means having vanes of screening material which are so formed as to be self-cleaning.

Other objects and advantages will be point- -ed out hereinafter in the description and in the claims appended thereto.

In the drawings, i

Fig. 1 illustrates a grinding mill in conjunction with a discharge device embodying my invention.

. Fig. 2 is an end view of the discharge device of Fig. 1, taken on line 2-2 of Fig. 1.

Fig. 3 is a section through thev discharge means, on line 3-3 of Fig. 1.

Fig. 4 is a perspective view of a portion of a mill with the discharge device.

Referring to-Fig. 1, the invention is illustrated in conjunction with a well known type of mill, although it is to be understood that the/invention has utility with other types of grinding mills.

As is well understood, the mill illustrated is adapted to be supported for rotation on trunnions 10, 11,'Which are hollow and through 1929. serial No. 379,897.

which material may pass. The scoop feeder 12 serves to feed material into the mill-through trunnion 10, and the material, pulverized Ato the desired ineness, passes out with the water or other liquid used in the grinding process at the discharge end 13. The millillustrated has a conical discharge portion 14 and, as is well understood, diii'erent sizes of material being ground Within the mill and the 'grinding media assume positions withinthis 4conical portion 14 in accordance with their relative sizes. That is, as the mill rotates, the larger particles become located in the vicinity of the cylindrical portion 15 of the mill, and the remaining material classifies'itself according to size, with the finer particles thereof graded toward and located at the discharge end of the mill. 'While mills of this type need not necessarily be provided with discharge means of the character about to be described,

it has become the'practice to operate grindingk mills under overload conditions, Vwith the result that coarse material (and sometimes halls) is likely to be discharged at the discharge end of the mill, and therefore, under these circumstances, it becomes desirableV to use discharge means which will prevent the discharge of coarse material and grinding media.

The discharge means of my invention comas in a radial plane or in .a plane not intersecting the center line of the mill.

Referring to Fig.v 1, the discharge means is so constructed as to function in a clockwise direction as viewed from the right. The vanes are made of screen material of such mesh, or of crossed wires so spaced, as to insure the separation of material of a coarseness greater than that desired as a product. The screening material 17 of, each vane is secured toone side of a grille 18 which in turn is mounted in place by means of bolts 19, 20 and 21, Fig. 1. The spacing of the bars of the grille is such as to protect the small perforations of the screening material from the impact of the balls and of coarse material. As the mill is rotated these bars come in contact with material which 4 has come from the grinding zone including any balls which may have happened to have dropped within the area occupied by the discharge means.

Since grille 18 of each vane is on the surface of a vane which faces upwardly when rising as the mill rotates, the grille 18 will save harmless the relatively tine meshes of the screen 17 from the action of balls or coarse material which might come within the area occupied by the discharge device.

The vanes 16 are setlsubstantially parallel to the flow of material outgoing from the mill, thereby affording substantially no restriction or interruption of the free How of material out of the mill.

The are vfurther characterized by their curve surfaces which have their concave sides facing upwardly as they rise when the mill rotates. The outer edge of each vane is in contact with the inner Wall of the drum and, by virtue of the curved form of each' vane, a scooping action is produced as it passes through material. This results in producing a partial cross-flow of material over the surface of a vane which tends to clean the meshes of the screen. A vane formed in the manner described utilizes its screen area to the best ladvantage as the scooping action a1- lows the fines to drain oif above the water level from portions of the screen which successively pass through a horizontal position.

Therefore, a small grate area used in this manner can do many times the work the same grate area could do if it were located below the surface of the material or liquid being screened.

I n order to permit overloading conditions in a mill of the character described, I provide a wall 22 which, in the embodiment of the invention illustrated, is in the form of a conical surface positioned reversely in respect to the discharge conical portion 14 of the mill. Wall 22 may be made of one piece, or may be made of a plurality of sections 23, as illustrated in Fig. 2, and, in any event, it may be secured to the shell of the mill by means of bolts 20.

Wall 22 is provided with a central opening 24 through which material and water within the mill may flow in its progress from` the mill. In cases in which it isidesired to maintain a low pulp line, additional ports such as ports 25 may be provided, in any number and size. When the mill is operating under overload conditions, it will be appreciated that balls or coarse material are likely to pass through opening 24 and come into contact with the discharge means just described. When such event occurs, such balls and material might be discharged fromy the mill if proper provision has not been made to return them to the grinding zone of the mill. In the present instance these balls and coarse material strike upon the grille 18, and, as the mill is rotated, they are scooped up into troughs 26, one of which is provided for each vane 16. These troughs are so sloped that when they have been rotated to a horizontal position the coarse material will start to gravitate toward the opening 24 of wall 22. The momentumv of the coarse material, and particularly of the balls, caused by the inclination which the troughs assume at or near their highest position of travel, is sutlicient to cause the balls to be carried Well backward into the grinding zone.

It will be noted that there is a clear passage straight through the mill, with the result that there is no impediment to the free flow'of material through the zone of the discharge means except to the extent which may be charged to the agitation and screening effect of the vanes themselves. Advantage is taken of the fact that the rate of flow through the zone o'f the discharge means is slower than the rate at which the vanes rotate, and therefore practically no material can pass out of the mill without having been subjected to the screening effect of the discharge means unless under exceedingly high overload conditions, under which conditions the rate of travel thrugh ther mill or through the zone of the discharge means is in excess of the rate at which the vanes move as the mill is rotated. Under this latter condition oversize material may be discharged, but this is an advantage since the discharge of oversize material constitutes a signal to an operator that the mill is overloaded beyond the point at which it can be grinding satisfactorily.

While I have, in many instances, in the description of my invention and in the claims, referred to balls as one form of grindin that I intend such reference to designate any kind of grinding media whatsoever, as, for example, balls, pebbles, bars, disks and kindred shapes of suitable material.

I claim:

1. In a grinding mill, the combination with a rotary drum, of a discharge device therein'having vanes comprising perforated material, and a wall separating the discharge device from the grinding zone of the mill, said wall being conical with its convex surface facing the grinding zone of the mill.

2. In a grinding mill, the combination with a rotary drum having a conical portion with its small end toward the discharge end of the mill, of a discharge device therein having vanes comprising perforated material, a wall separating the discharge device from the grinding zone of the mill, said wall having an opening at its midpoint permedia, I wish it to be understood device from the grindin mitting the flow of material from the grinding zone of the mill to the discharge device, and means for receiving coarse material and balls from said vanes which has passed through said opening from the grinding zone. l

3. The combination set forth in claim 2 in which the means for receiving coarse material and balls from the vanes comprises troughs, one of which is associated with the inner edge of each vane.

4. In a grinding4 mill, the combination with a rotary drum, of a discharge device therein having vanes comprising perforated material, a wall separating the discharge zone of the mill, said wall having an opening at its midpoint permitting the flow of material from the grinding zone of the mill to the discharge device, andtroughs at the inner edges of said vanes, one of said troughs being provided for each of said vanes and having one side in continuation of its associated vane and another side sloping in respect to the axis of the mill so as to return oversize material and balls to the grinding zone as the trough rises during the rotation of the mill.

5. In a grinding mill, the combination with a rotary drum, of a discharge device located at the discharge end of the mill and having perforated vanes for screening material coming into contact therewith, each of said vanes being mounted to rotate with the mill and formed so that substantially all portions of its surface leave the flow of material with theouter surface extending upwardly at an angle to the surfaceof the material flowing from the grinding zone to the discharge end of the mill. y. Y

6. In a grinding mill, the 'combination with a rotary drum, of a discharge device through which material flows to the discharge end of the mill and having perforated vanes for screening material coming into contact therewith, said vanes being concave with the concave surface thereof facing upwardly when rising as the drum rotates and extending a direction lengthwise of the mill whichfis substantially longitudinal of the flow of material by the discharge device.

7. In a grinding mill, the combination with a rotary drum, of a discharge device located at the discharge end of the mill and havingperforated vanes for screening material coming into contact therewith, said vanes comprising screening and a grille on the side of the screening which faces upwardly when rising as the drum rotates.

8. In a grinding mill, the combination of a rotary drum and screening means having a perforated device for screening material to be discharged from the mill, said device comprising a curved vane mounted to rotatev with the mill, the surface of the vane which extends toward the axis of rotation, being substantially radial with the axis of rotation and the end furthest away from the axis of a rotary drum and screening means having a perforated device for screening material to be discharged from the mill, said perforated device comprising a vane extending inwardly from the wall of the mill, a wall separating the screening device from the grinding zone of the mill, and means for receiving oversize pieces of material from said perforated device as the mill is rotated and for directing the oversize pieces though the opening in the separating wall.

10. In a rinding mill, the combination of a rotary rum having a conical discharge end open at its small end, a dischar e device located within the conical disc arge end, said discharge device comprising a perforated vane having perforations therein for' screening material leaving the mill, the surface of said vane bin curved, a wall separating the discharge evice from the grinding zone of the mill and protecting the perforated vane, said wall having openings for the passage of material, and means bordering the inner line of said vane for receiving material from the vane and for directing the same through one of said openings to the grinding zone of the mill.

11. In combination, a rotary grinding mill through which material advances along the axis of the mill as it is being comminuted, and a screening device interposed in the path of travel of the material leaving the grinding zone of the mill, said screening device comprising a plurality of perforated members extending lengthwise of the mill and from the wall of the mill toward its axis but leaving spacev at opposite sides and at the free ed es of the perforated members, said space orming unobstructed passageways through the screening device through which material may pass the screening device without being screened.

12. In combination, a rotary grinding mill having an inlet opening at one end and a discharge opening at its other end and through which material advances as it is being comminuted, a screenin device at its discharge end comprising at east one perforated member extending lengthwise of the mill and from the wall of the mill toward the axis but terminating short thereof, and a perforated wall between the grinding zone device so that of the mill and the screem'rg e screening dethe entrance of material to 

